Pneumatic tool



Aug. 28, 1962 A. J. SMITH PNEUMATIC TOOL Filed March 27, 1959 3 Sheets-Sheet 1 Arthur J. .Sm/'fh INVENTOR.

Aug. 28, 1962 Filed March 27, 1959 A. J. SMITH 3,051,135

PNEUMATIC TOOL 3 Sheets-Sheet 2 Arf/wr J. iSwim INVENTOR.

BY @www v ana/#way M@ A. J. SMITH PNEUMATIC TOOL Aug. 28, 1962 s sheets-sheet s Filed March 27. 1959 Arf/zur. .Sm/7h `1N VEN TOR.

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United States Patent O 3,051,135 PNEUMATIC TGOL Arthur J. Smith, Visalia, Calif., assigner, by mesne assignments, to Bostitch Industrial Stapling Machine C0., East Greenwich, RJ., a corporation of Rhode Island Filed Mar. 27, 1959, Ser. No. 892,368 16 Claims. (Cl. 121-21) This invention relates to an impact tool and more particularly to pneumatic impact tools for driving staples, nails or other fasteners.

An object of the invention is to provide a pneumatic impact tool which is light, portable and capable of driving fasteners eiiectively with a minimum of air pressure.

The pneumatic tool is made as a gun for driving fasteners, although the same principles involved in the operation of the gun-type tool, may be applied to other types of fastener driving equipment. To facilitate the description, the portable tool is `selected `as a preference with the understanding that the invention is capable of being embodied in various apparatuses.

The portable tool has a hollow body provided with a chamber that is constantly exposed to line pressure, together with a trigger operated valve assembly controlling a network of air conductors. Air under pressure passing through the controlled conductors, is used to actuate a hollow poppet, one of the functions of which is to communicate the lpressure chamber with a second chamber occupied by the head of the poppet. As the poppet moves the head becomes unseated from its rest position, opening a port which registers the chambers.

A driver assembly has the larger of fa pair of pistons located in the second chamber so that when the poppet is moved to the port opening position a driver assembly commences its stroke. Upon completion of the driving stroke, the driver mechanism is pneumatically returned to the poised position, and the last portion of the return stroke is pneumatically buttered by a unique buffering system built in the tool.

A more specific object of this invention is to provide a pneumatic tool of a general type discussed above wherein there are pneumatic means to return the driver assembly to its poised position in such a manner that it is unnecessary to exhaust the air that has returned the driver assembly to its poised position when the tool is actuated. In other tools of this general class it is necessary to have a complicated venting mechanism that will exhaust this air to the atmosphere at the moment the tool is actuated in order to eliminate the opposing Iforce that the air would oiier. In still other tools this air under consideration is not exhausted, but the force that is holding the driver assembly in its poised position reduces the effective driving -force on the driver assembly by the same amount.

A further object of the invention is to provide a pneumatic impact tool, again of the same general type discussed above, wherein the effective driving area that the air acts upon in moving the driver assembly forward, is equal to the area of the diameter of the lbore in which the driver piston operates. This piston was said to be located lin the second chamber, but it is to be emphasized that even though this piston has a stem connected to it, the stem cross-sectional area plus a smaller diameter piston on that stem has air applied under pressure thereon at the same time that air is applied under pressure to the larger piston in the second chamber so that the pressures on both the smaller and larger pistons are additive with the summation being at least equal to the crosssectional 'area of the second chamber which has the larger diameter piston located in it. In other tools of this type, the etective driving area of the piston is re- Y:ce

duced by the area of the diameter of the driver piston stem, plus the force that is holding the driver assembly in its poised position, if the air is not exhausted before the tool is tired. Again, other tools use a spring to return the driver assembly, and the force acting upon the driver assembly Aand moving it forward is reduced by the opposition ot'fered by the spring. This invention `eliminates all of these parasitic forces to achieve one of the principal objectives of the invention which is to attain maximum lthrust on the fastener for agiven pneumatic pressure input.

The driver assembly larger diameter piston is limited in its travel by engaging a shock bumper disposed in la second chamber of the tool body. The shock bumper will ordinarily be constructed of rubber or some other elastomeric substance and may possibly deteriorate or otherwise break down. Shock vburnpers determining the extent of movement of the driver assembly in a tool of this type, are not new. However, upon failure of shock bumpers in previous tools, serious damage to the driver assembly and other parts of the tool has resulted. An important feature of the invention is the structural arrangement enabling the tool to {shut-down automatically upon failure of the shock bumper thereby eliminating eX- pensive repairs that would undoubtedly result if the tool continued to operate after the shock bumper failed.

Most tools `ot' the type under discussion have valve assemblies for controlling the admission of air under pressure into the working chamber of the tool. To my knowledge no substantial etorts have been made to facilitate operation of the valve assembly. A further object of this invention is to provide pneumatic means to reduce the eiort that is required to actuate the valve of the valve assembly and to automatically i.e. by pneumatic means, return the valve and the valve assembly to the valve closed position. It is to be understood that the valve of this tool is a multipurpose valve. The closed position is established by having the valve prevent air under pressure from passing into the network of air conductors from the main pressure chamber of the tool, although in this position air under pressure which has served its purpose of actuating the driver assembly, may be exhausted to the atmosphere, through a section of the valve assembly. When the valve assembly is in the open position or what is arbitrarily considered an open position, the valve member seals ott the atmospheric port or vent and at the same time admits air under pressure from the main pressure chamber, through the air conductor network to the poppet and driver assemblies of the tool.

A feature of the tool enables the tool to be more smoothly operative by preventing high rates of deceleration of the driver assembly when it is being returned to the poised position. There is a comparatively small diameter cylinder in the tool body which accepts a part of the small diameter piston of the driver assembly. There is a clearance between the small diameter piston and the side wall of the cylinder, this clearance functioning as an orifice to allow bleed air to pass between the surface of the cylinder and the surface of the piston. The stem of the driver assembly is provided with an air conductive passage extending through it and through which the air used for driving the driver assembly is exhausted. During the return Stroke of the driver assembly the last mentioned air continues to exhaust through the hollow driver assembly stem, but the rate of exhaust is severely reduced when the small diameter piston enters the cylinder to form a dashpot, or at least, to have the small diameter piston and cylinder function as a dashpot wtih the air compressing in the cylinder and bleeding past the cylinder and piston side fwalls due to the clearance therebetween. Accordingly, the last portion of the return motion of the driver assembly is arrested without the accompanying attenuation of shocks. Furthermore, ysince in the poised position the small diameter cylinder has its face contained within the cylinder, and the initial operation of the tool has air under pressure adjacent to this small diameter piston, this initial actuation air cannot contact the driving face of the small diameter piston. In the structural organization the only parts, aside from the valve assembly and inner surfacesof the tool body, that the-'air underpressure engages are those of the poppet assembly deiinitely requiring the poppet assembly to be initially actuated before the driver assembly begins to move. No only does the small diameter cylinder function as a part of a shock attenuating device, but it also assures that the small diameter piston of the driver assembly is protected against receiving air under pressure against Yits Working face until the poppet assembly is properly moved as the initial step in the driving stroke of the tool.

Theseand other objects, features and advantages will be explanied further in the details of construction and operation that follow: Y

FIGUREl is a perspective view of the tool. L. FIGURE Y2 is alongitudinal sectional view taken on the line 2-2 of-FIGURE l showing the driver assembly and poppet in a poised or rest position.

FIGURE 3Y is a transverse sectional View taken on the line 3-3 of FIGURE 2. Y

FIGURE 4 is a sectional view taken on the line 4-4 of FIGURE y2. g f

Y FIGURE 5 is a fragmentary sectional view similar to FIGURE 2 but showing pneumatic ow conditions as they exist when the poppet assembly has just opened and thedriver assembly is beginning its driving stroke.

FIGURE 6 is a fragmentary sectional view similar to FIGURE 5 but showing an instantaneous position of the driver assembly and poppet as the fastener has been driven from the magazine.

FIGURE 7 is a fragmentary sectional viewsimilar to FIGUREG showing the valveassembly which has been pneumatically closed and showing the return flow of the air through the stem of the driver assembly.

FIGURE 8 isa fragmentary sectional View showing failure of'the shock bumper at the lower part of this figure.

` Pn eumatic impact tool V11), FIGURES l and 2, may vary in configuration.V The tool has a body 12 provided nular groove thereof, is attached to stem 32 e.g. by being integral therewith, and is movable with the valve stem 32 to a position at which port 56 is closed (FIGURE 5) when the valve assembly is in the open position, i.e. valve element 48 unseated. It is evident now that the network 54 of air conductors no longer is open tothe atmosphere through vent 62, but sub-chamber 58 becomes j registered with the main pressure chamber 14 so that air from the main pressure chamber may pass through the valve assembly, sub-chamber 58, network 54 and enter a chamber 7i? which is 4subsequently referred to a third chamber. Y

The internal cavity of hollow body 12 has a second chamber 72 divided from chamber 14 by a port 74. The port is a central opening in a partition 76 extending across body 12. Poppet assembly '78 is `disposed in part in chamber 14 and in part inrchamber 72. Poppet 80 has a hollow shank 82. Head 8 4 provided 'with annular seal 86 disposed on a seat of port 74 is at the lower end of poppet'8i, and there is a piston 88 at the opposite end of poppet 80. The piston 88 is bolted as at 89 to a flange 90 en poppetSil, and there is a gasket 92 be- 1 tween flange 90 and pistonSS. O-ring 94 is carried by.a

with Aa first chamber 14 and an opening 16 registered with the chamber and'adapted to connect with a pneumatic pressurev source through a pneumatic pressure line 18. First chamber 14 is composed of a part of the valve 20 f body 12 and handle 22 of the same body when a gunltype configuration is selected. Trigger 24 is freely pivotally mounted on a body carried spindle 26, and the trigger has a wear pin28 which contacts one'end of valve assembly 30. The valve assembly consists of a valve stem 32 yhaving heads 34 and 36 of-equal diameter at opposite ends thereof. There is an annular groove containingO-rings 38 and 40 in each head 34 and 36 and these together -with portions of the heads areoperable in bores 42 and 44 in body 12 and hollow plug 46 thereof, respectively. Bores 42 and 44 are coaxial, and bore 44 constitutes part of means to be more fully described subsequently, for returning the valve of valve assembly 30 to the closed position after it is manually opened by actuating trigger 24. Stem 32 has a valve element 48, preferably of rubber, and this is disposed on valve seat at one end of valve chamber 52. The valve chamber is in registry with a network 54 of said conductors formed in body 12. Port 56 divides chamber 52 into sub-chambers 58 and 60 with the sub-chambers being in registry when the valve assembly is closed (FIGURE 2.) Opening 62, see FIGURE 4, in body 12 registers with `subchamber -60 and constitutes a vent to the atmosphere. A cylindrical valve element 64 having O-ring 66 in an angroove in piston 88 and works against the inner Surface of chamber 14 above shoulder 96 which protrudes inwardly of the cylinder part of chamber 14 occupied and transversed by piston 88.

Driver assembly 98 is located in part within hollow poppet and in part within chamber 72. The driver assembly has a blade 100 operable in passage 102 of nose 104 that is bolted .to the lower end of body 12 Aand which closes the lower` end of chamber 72. -Nose 104 -has a conventional magazine 166 connected with it for automatically feeding fasteners 108 into passage 1,02 so that they may be .driven :by blade 11N) in response to operation of the driver assembly 98.

.In addition to blade 100 driver assembly 98 includes hollow stem V11i) disposed longitudinally within poppet 80 and spaced from the inner ysurface thereof to yform por- .tions of .the Vside walls of chamber 114. Since stem 110 is hollow it has a passage 116 extending longitudinally therethrough with the upper end of passage116 being open andV the lower end portion being in registry with a lateral oriice 118. A comparatively small diameter piston '122 issecured to the upper end of stem 110 and has an O-ring 124 located in an annular groove therein. The piston 122 may be threaded or otherwise secured to stem 110. A comparatively large diameter piston 126 is iitted on the lower end ofstem 110 and located beneath head `84 Vof poppet assembly 78 and within the bore of body 12 which constitutes the major part of chamber 72. The piston 126 has an lO-ring 128 disposed in an annular groove -on the side surface thereof, and there are means for lockingpiston 126 in place. These means includes lateral ange 132 at the lower extremity of stem 110 which constitutesan abutment for a piston 126, together with nut 134 threaded on a part of stem 110 and which bears against the upper surfaceof piston 126. Blade is .fastened to the stem by ytransverse pin 136 which is locked in placeby piston 1,26 covering the ends thereof. O-ring 138 held in place by retainers 140, engages the outer surface of stem 110 and is carried lby the lower part of poppet 80.

To facilitate manufacture and assembly ythere i-s a cap bolted .to a remainder of the body 12, and the cap has a cavity constituting the end wall `and at least a portion of the'side wall chamber 70. Cylinder 152Vy is fixed to the cap 150 andis coaxial with poppet 80. The cylinder is slightly larger lin diameter than the small diameter piston 122 leaving a clearance between the surfaces of cylinder 152 and piston 122 `so Ithat air may may be bled therethrough into chamber 70,. Cylinder 152 and piston 122 serve -several purposes which have been described previously. A plurality of ports 158 are formed in the poppet near the lower end thereof, and they communicate chamber'114 with the chamber 14 at all times. The shock bumper is an annular ring of fiexible material, for instance rubber or certain plastics having properties of rubber. Bumper 166 is located at the lower end of the second chamber 72 and is contacted :by the lower face of piston 126 during the downward movement of the piston 126, this establishing the end of a driving stroke for the driver assembly 98.

In operation, air under pressure enters chamber 14, and this chamber is continually under line pressure throughout the complete use of the tool. This air surrounds poppet assembly 7S and applies pressure on the enlarged part of valve stem 30 containing valve element 4S sealing it -against its seat Sil Iand -thereby prevents air from passing through air conductor network 54. In other words, the valve assembly 39 is pneumatically held in lthe closed position. `O-ring dil prevents air from enteru ing chamber 45 that was previously mentioned as being constructed in plug do. Since piston 8S of poppet assembly 73 is larger in diameter than head 84 and its seal 86, the air under pressure in chamber 14 maintains the poppet closed, isolating chambers 14 and 72. Air is free to enter ports 15S of poppet 80' and chamber 114i-, this air forcing against the lower end of the small diameter piston 122 and holding the driver assembly in an upper position against its stop created by partition 76 and piston 126.

To actuate the tool the operator pulls trigger 24 which removes valve element 43 Ifrom seat Sil as the valve assembly begins to open `that is, move upwardly with reference to the tool as oriented in the drawings. The eliort that is required .to pull the trigger and remove valve element 48 from seat Sti is reduced since chamber 45 is free of air pressure. As the valve `stem 32 continues to move in the same direction, plunger 54 enters and closes port 56 thereby isolating the sub-chambers 53 and d@ (FIF- URE rl'he opening of the valve permits air to pass through port 51 controlled by valve element 48, and air is enabled to ilow :through sub-chamber 5S, network 54 and enter the third chamber 7 G. As the `air continues -to enter chamber 79 it is partially restricted from entering fourth chamber 153 dened by the wall of cylinder 152, a part of cap 159 and the working face or the small diameter piston 122, since the air must pass through a narrow clearance -between small diameter piston 122 and the bore of cylinder 152. This restricted iiow of air entering chamber 153 prevents the air pressure from increasing rapidly in this chamber and moving the driver assembly forward before the rapidly increasing -air pressure in chamber 70 moves the poppet assembly 78 forward.

Air under pressure in third chamber 70 reacting on the working face of piston 88, this piston constituting a movable wall of cham-bers 14 and 7h respectively, moves the poppet assembly 7S forward with the air in chamber 14 passing through port 74 and contacting one of the working faces of the langer diameter piston 12d of driver assembly 9S. This begins to move the driver assembly forward, and as this assembly continues :to move forward, piston 122 leaves chamber 153 and air under pressure from third chamber 7d is applied to the upper face of the driver assembly piston 122. yFrom this point on (FIG- URES 5-7) to the remaining forward travel of the driver assembly, the total effective driving area that `the air is acting upon the moving and driver assembly in a forward direction, is equal to the cross-sectional area of the bore which defines chamber 72. rl`he lower end of blade 1% removes a single -fastener from magazine 1% and the nose 104 guides the fastener' as it is driven into its receiving Vmember until piston 126 contacts shock bumper 166 and completes the drivingcycle (FGURE 7).

As the driving cycle is completed, the air throughout the tool rbecomes static, and the forces acting upon poppet assembly 78 and tending to move -it downward are equal to the forces acting upon poppet assembly tending to move it upward. As the operator releases trigger 24, the air pressure that entered chamber 45 during the driving cycle by way of passage 17@` that opens laterally through the valve stem on the Valve chamber side of the valve member 48 and that opens into chamber 45, forces the valve assembly toward .the closed position. The valve assembly would not move from its open position if chamber 45 Were not pressurized in this way, since the yforces acting upon the valve assembly 36 and tending to move it in either direction would be equal. Plungers 36 and 34 are of equal diameter thereby having equal pressures thereon so Ithat the air passing through passage 17) and entering chamber 45 is sufficient to pneumatically return the valve of assembly 3G to the closed position.

As the valve assembly continues to move toward the closed position the air in chamber 45 is exhausted through vent 62 by passing through passage 170 and chamber 52. Air under pressure acting upon the surface of the valve assembly containing valve element 48 holds the valve assembly closed and prevent-s air in chamber 14 from exhausting to the atmosphere. At the same time air in chamber 7) is exhausted through network 54 to the atmosphere by way of the vent 62. As this air is being exhausted from chamber 70, additional air is entering this chamber from chamber 72A which is actually the portion of chamber 72 between piston 126 and port 74. The air in chamber 72A passes through port 1.18, passage 116' and into chamber 7h. Since passage 11'6 is smaller in diameter than the air conductor of network 54 leading from chamber 70 to the atmosphere, there is a reduction in air pressure in chamber 70 below 4the air pressure in chamber 14. Therefore, the high pressure in chamber 14 forces poppet assembly 78 upward until port 74 is closed and prevents additional air from entering cham-ber 72A. The remaining air in chamber 72A is exhausted Ito the atmosphere and the air pressure in chamber 114 forces the driver assembly 98 rapidly up- Ward by reacting on one face of piston 122. The driver assembly continues to move rapidly until piston 122 begins to enter chamber 153. At this point chamber 153 is formed and partially restricts the further leaving of the chamber and buffers or attenuates the impact of piston 126 contacting its stop.

FIGURE 8 shows the relative positions of the driver assembly 98 and poppet assembly 7S after trigger 24 is released, if the shock bumper is damaged or other wise fails. The shock bumper 160 allows the driver asysembly to continue its movement beyond its normal or predetermined stop position. Piston 88 of the poppet assembly is smaller in diameter than drive piston 126, therefore, when the driver Vassembly moves forward beyond its predetermined stop position and the trigger is released, the poppet assembly moves upward until lower end of chamber 114 contacts piston 22. The poppet assembly is unable to move upward beyond the position shown in FIGURE 8, since chamber 72 remains pressurized and the force holding the driver assembly forward is greater than the force acting upon the poppet assembly and tending to move it upward. The lower portion of piston 122 functions as a stop to limit the upward travel of the poppet assembly if the shock bumper fails.

The poppet assembly and driver assembly wil-l remain in a lowered position (FIGURE 8) and air will continue to exhaust to the atmosphere through vent I'62 until the air supply is disconnected from the tool. The automatic discontinuing of tool actuation in this way prevents damage to other parts of the tool, and only exists when shock bumper 160 fails or becomes damaged from use. The replacement of the damaged shock bumper will restore the tool -to its normal condition.

The foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly all suitable modifications and 7 equivalents may be resorted to, falling within the scope of the invention as claimed.

What is claimed as new is as follows:

1. In a pneumatic impact tool, a body having a first air chamber and an opening in registry therewith for connection with ya source of air under pressure, a second chamber in said body, a port separating said chambers, a hollow poppet having a piston at one end operable in said first chamber and forming -a movable wall ,thereof and a head at the opposite end normally closing said port and isolating said chambers, a driver assembly reciprocatable in said hollow poppet, a third chamber in said body with said piston forming a movable `wall thereof, a valve assembly carried by said body, an airconductor network controlled'by said valve assembly land establishing communication betweensaid first chamber and said third chamber to thereby enable air to enter said third chamber and move said poppet in` one direction, said driver assembly including a stem with a smaller piston at one end and operable in said hollow poppet, a larger piston onsaid stem and disposed in said second chamber and moved by air under pressure passing through said port, a cylinder forming a fourth chamber in said third chamber and accommodating said smaller piston, said'smaller piston being withdrawn from said cylinder as said driver assembly begins to move thereby subjecting one side of said smaller piston to pressure from said third chamber, said poppet having a port registered with said rst chamber which communicates said first chamber with the opposite side of said smaller piston and thereby returns said driver assembly when said first and .second chamber are isolated, during which movement said smaller piston re-enters said cylinder and creates a back pressure to buter the return movement of said driver assembly.

2. Thegtool of claim l wherein the total effective area of said one side of said smaller piston and said larger piston is at least equal to the cross sectional area of the portion of said second chamber in which said larger piston is operable. Y

3. In a pneumatic impact tool, a body having a first air chamber and an opening in registry therewith for connection with a source of air Yunder pressure, a second chamber in said body, a port separating said chambers, a hollow poppet having a piston at one end operable in said first chamber and forming a movable wall thereof and a headrat the opposite end normally closing said port and isolating said chambers, a driver assembly reciprocatable in said hollow poppet, a third chamber in said body with said piston yforming a movable wall thereof, a valve assembly carried by said body, an air conductor network controlled by said valve assembly and establishing communication between said rst chamber and said third chamber to thereby enable air to enter said third chamber and move said poppet inV one direction, said driver assembly including a stem with a smaller piston at one end and operable in said hollow poppet, a larger piston on said stem and disposed in said second chamber and moved by air under pressure passing through said port, a cylinder forming a fourth chamber in said third chamber .and accommodating said smaller piston,

said smaller piston being lwithdrawn from said cylinder as said driver assembly begins to move thereby subjecting one side .of said smaller piston to 4pressureff'rom said third chamber, said poppet having a port registered with said iirst chamber to communicate said rst chamber with the opposite side of said smaller piston, said stem having an air return passageway extending longitudinally thereof and through which the air which has driven said driver assembly is returned for exhausting throughV a portion'of said network controlled by said valve assembly.

4. In a pneumatic impact tool, a body having a first air chamber and an opening in registry therewith for connection with a source of air under pressure, a second 8 s chamber in said body, a port separating said chambers, a hollow poppet having a piston at one end operable in said first chamber and forming a movable wall thereof and a head at the opposite end normally closing said port and isolating said chambers, a driver assembly reciprocatable in said hollow poppet, a third chamber in said body with said piston forming a movable wall thereof, a valve assembly carried by said body, an air conductor network controlled by said valve assembly and establishing communication between said first chamber and said third chamber to thereby enable air to enter said third chamber and move said poppet in one direction, said driver assembly including a stem with a smaller piston at one end and operable in said hollow poppet, a larger piston on said stem and disposed in said second chamber and moved by air under pressure passing through said port, said poppet having a port in registry with said iirst chamber to admit air into said hollow poppet on one side of said smaller piston and return said driver assembly, a resilient cushion in said body and engaged by said larger piston to establish a predetermined end of a driving stroke of said driver assembly so that if said driver assembly over-travels said predetermined end of 'the driving stroke said smaller piston also oveitravels and forms a stop for the poppet assembly and preventing it from commencing its return with the consequence that said second chamber remains pressurized and said driver assembly remains in a non-returned position.

5. In a fastener driving tool, a body provided with a first chamber, a second chamber, said tool body having a port between said chambers, la poppet assembly having a poppet with a head closing said port and isolating said chambers when said poppet assembly is in a position corresponding to the poised position of the tool, a driver assembly including a Stem, said poppet being hollow with said stem located therein and movable with reference to said poppet, said stem having means by which to couple a driver element thereto, a piston constituting part of said poppet assembly and located in said rst chamber and constituting a movable wall of a third chamber in said body, a valve assembly carried by said body to admit air yfrom said iirst chamber to said third chamber and thereby move said poppet assembly in -a direction to open said port, said driver assembly having a larger diameter piston located in said second chamber, the last mentioned piston being movable by air under pressure entering said second chamber from said iirst chamber when said port is opened and thereby propelling said driver assembly, land pneumatic means including a smaller diameter piston attached to said stem and located in said hollow poppet for returning said driver assembly, a pneumatic buffer operatively associated with said smaller diameter piston for attenuating the return motion of said driver assembly, said pneumatic buer including a cylinder within which said smaller diameter piston is received at the end of the return stroke of said driver assembly, said cylinder and smaller diameter piston having clearance therebetween 'to allow leakage of air under pressure, said stem having a longitudinal passageway registering the lower end of said stem with the portion of said second chamber traversed by said larger diameter piston when said Idriver assembly is in its driving stroke so that upon return movement of said driver assembly the air previously used for propulsion of said driver assembly is exhausted through said passageway of said stem and said third chamber.

6. In a fastener driving tool, a body provided with a first chamber, a second chamber, said tool Ibody having a port between -said chambers, a poppet assembly having a poppet with a head closing said port and isolating said chambers when said poppet assembly is in -a position corresponding to the poised position of the tool, a driver assembly including a stem, said poppet being hollow with said stem located therein and movable with reference to said poppet, said stem having means by which to couple a driver element thereto, `a piston constituting part of said poppet assembly and located in said first chamber and constituting a movable wall of a third chamber in said body, a valve assembly carried by said body to admit air from said rst chamber to said third chamber and thereby move said poppet assembly in a direction to open said port, said driver `assembly having a larger diameter piston located in said second chamber, the last mentioned piston being movable by air under pressure entering said second chamber from said first chamber when said port is opened and thereby propelling said driver assembly, and pneu| matic means including a smaller diameter piston attached to said stem and located in `said hollow poppet for returning said driver assembly, a pneumatic buffer operatively associated with said smaller diameter piston for attenuating the return motion of said driver assembly, said pneumatic buffer including a cylinder within which said smaller diameter piston is received at the end of the return stroke of said driver assembly, said cylinder and smaller diameter piston having clearance therebetween to allow leakage `of air under pressure, said stem having a longitudinal passageway registering the lower end of `said stem with Ithe portion of said second chamber traversed by said larger diameter piston when said driver assembly is in its driving stroke so that upon return movement of said driver assembly `the air previously used for propulsion of said driver assembly is exhausted through said passageway of said stem and said third chamber, said smaller `diameter piston lbeing movable from said cylinder as said stem begins its driving stroke with said driver assembly and thereby becoming exposed to the pressure in said third chamber so that the total force applied .to the driver assembly is attained from the summation of pressures on said larger diameter piston and smaller diameter pistons.

7. In a fastener driving tool, a body provided with a first chamber, a second chamber, said tool body having a port between said chambers, a poppet assembly having a poppet with a head closing said port and isolating said chambers when said poppet assembly is in a position corresponding to the poised position of the tool, a driver assembly including a stem, said poppet being hollow with said stem located therein and movable with reference to said poppet, said stem having means by which to couple a driver element thereto, a piston constituting part of said poppet assembly and located in said lirst chamber and constituting a movable wall of -a third chamber in said body, a valve assembly carried by said body to admit air from said first chamber to said third chamber and thereby move said poppet assembly in a direction to open said port, said driver assembly having a larger diameter piston located in said second chamber, the last mentioned piston being movable by air under pressure entering said second chamber from said first chamber when said port is opened and thereby propelling said driver assembly, and pneumatic means including a smaller vdiameter piston attached to said stem and located in said hollow poppet for returning said driver assembly, a pneumatic buffer operatively associated with said smaller diameter piston for attenuating the return motion of said driver assembly, said poppet having a port in registry with said first chamber and in registry with the space between the inner surface of said poppet and the outer surface of said stem so that air entering said space reacts on a face of said smaller diameter piston to return said driver assembly after the pressure in said first charnber has returned said poppet to the position at which said poppet closes the first mentioned port and thereby prevents pressure of said first chamber from further reacting on said larger diameter piston.

8. The tool of claim 7 wherein there is a shock bumper in said second chamber against which said larger diameter piston contacts to establish the limit yof travel of said driver assembly in one direction, said shock bumper being flexible.

9. The tool of claim 7 wherein there is a shock bumper in said second chamber against which said larger diameter piston contacts to establish the limit of travel of said driver assembly in one direction, said shock bumper being flexible, and means operable when said bumper is flexed beyond a predetermined limit enabling overtravel of said driver assembly for discontinuing operation of the driver assembly.

10. In a pneumatic impact tool, a body having a first air chamber and an opening communicating therewith for connection with a source of air under pressure, a second chamber in said body axially alined with the first chamber, a port separating said chambers, a reciprocable poppet comprising a hollow stem having a piston at one end operable in said first chamber and forming a movable wall thereof and -a head at the opposite end operable in the second chamber to normally close said port and isolate said chamber, said piston being subject to the pressure in the first chamber at all times, a driver assembly reciprocable in said hollow poppet stem, a valve assembly carried by said body, an air conductor network controlled by said valve assembly for establishing communication between said first chamber and the upper side of said poppet piston to thereby enable pressure air to move said poppet in one direction and `open said port, the upper side of said piston having a greater effective area than the underside thereof, said driver assembly including a stem with a small piston at one end and `operable in said hollow poppet stem, a larger piston on said driver assembly stern disposed in said `second `chamber and moved in one direction by air under pressure passing through said port from said rst chamber, said poppet stem having an lopening in constant communication with said first chamber to admit pressure air into said hollo-w poppet stem `on the driver assembly `stem side of said small piston for moving said driver assembly in the opposite direction upon the closing of said port.

l l. In a pneumatic impact tool a body having a first air chamber and an opening communicating therewith for connection with -a source of air under pressure, a second chamber in said body axially aligned with the first chamber, a port separating said chambers, a poppet comprising a 'hollow stem open from end-to-end and having a piston at one end roperable in said first chamber and forming a movable wall thereof, a head at the opposite end of said poppet stem normally closing said port from the second chamber side thereof to isolate said chambers from each other, said piston being subject to air lpressure in said first chamber at all times, a driver assembly reciprocable in said hollow poppet stem, a valve assembly carried by said body, an air conductor network controlled by said Valve assembly for establishing communication between said first chamber and the upper side of said piston to enable air pressure to move said piston and poppet stem in one direction against the pressure in the first cylinder to open said port, means for limiting the port opening movement of said poppet, said driver assembly including a stem with a small piston at one end and operable in said hollow poppet stem, a larger piston on said driver assembly stem disposed in said second chamber and moved in said one direction from an initial positionv by Vair under pressure passing through said port, said poppet stem having a side wall opening in constant communication with the first chamber to admit air pressure into said hollow poppet stem on the driver stern side of said smaller piston for returning said driver assembly to its initial position when said port is closed.

12. In a fastener driving tool, a -body provided with a rst chamber, means for supplying air under pressure to said first chamber, a second chamber axially alined with the first chamber, said tool body having a port between said chambers, a poppet assembly comprising a stem having a head at one end for closing said port from the second chamber side thereof and isolating said chambers, said stem extending from said head into said first chamber, a driver assembly in said second chamber `and including a stem, said poppet stem being hollow and `forming an open ended cylinder with said `driver assembly stem located therein and movable with reference to said poppet assem-V bly, said driver assembly Ystern having means by which to couple a driver element thereto, a piston constituting a part of said poppet assembly lstem and located in said rst chamber to provide a movable Wall of a third chamber in said body, said poppet assembly being normally'urged to the port closing position -by the air pressure in said irst chamber acting on said poppet piston, a normally closed valve assembly carried by said body and adapted when opened to admit air from said first chamber to said third chamber and thereby move said poppet assembly in a direction to open said port, the third chamber side of said piston being of greater elective area than the irst chamber side of the piston, means for limiting the port opening movement of said poppet, said driver assembly having a large piston located in said second chamber, the last mentioned piston being axially movable relative to said poppet assembly by air under pressure entering said second chamber from the rst chamber when said port is opened for propelling said driver assembly in one direction from an initial position, and pneumatic means including a smaller piston attached to said driver assembly stem and located in said poppet stem cylinder for returning said driver assembly to its initial position when said port is closed.

13. The combination of claim including buffer means in said second chamber cooperating With said langer piston to cushion the driving stroke of said driver assembly, and means operable upon excessive movement of said larger piston on said dn'ving stroke to unseat said poppet head and prevent further operation of said driver assembly.

14. In an impact tool having a pair of axially aligned irst and second cylinders and including a port for separating said cylinders and means for maintaining the irst cylinder in continuous communication with a pneumatic pressure source, acombination valving'and driving 'unit for operation withinsaid cylinders comprising a poppet havingra hollow stem anda driver having a stem slidable 'coaxially in the hollow sternl of theY poppet, Ysaid poppet stem having a head at one end adapted to close said port from the second cylinder side thereof and a'piston at its opposite end pneumatically operable in the first cylinder, said driver assembly having a large piston at one end of its stem for pneumatic operation in said second cylinder and a smaller piston at the other end yof its stem slidably fitted in the hollow stern of said poppet, said hollow poppet stem having a side wall opening adjacent said head for continuous communication of pneumatic pressure in said first cylinder with the interior of the poppet stem and said smaller piston, and means Within said poppet stem for sealing the driver stem against leakage of pneumatic pressure therealong from said side `wall opening to said second chamber.

l5. The valving and driving unit defined in claim 14 wherein the driver stem has a longitudinal passage extending lfrom its small piston end to a lateral opening adjacent said large piston.

16. The valving and driving unit defined in claim 14 wherein said hollow poppet stem is provided with internal stop means to engage said smaller piston and limit the coaxial sliding movement of said driver stem relative to said -poppet stem under the influence of said large piston.

References Cited in the lile of this patent UNITED STATES PATENTS 2,699,102 Doyle et al L Jan. 11, 1955 2,854,953 Osborne Oct. 7, 1958 2,872,901 Goldring et al Feb. 10, 1959 2,923,937 p Laucher Feb. 9, 1960 2,960,067 Osborne Nov. l5, 1960 am. (ma er.

UNITED STATES vPATENT OFFICE CERTIFICATE 0F CORRECTION Patent No., 3,051, 135 August 28, 1962 Arthur .L Smith It is hereby certified that error appears in the above .numbered patent requiring correction and that the said Letters Patent should read as corrected below. y

Column 2, line 69, for "wtih" read with column 3, line 13, for "No" read Not line 69, for "said conductors" read air conductors --g column 5,"1`ig'1e'sir 61 and 62, for FIGURES read FIGURE column 6, line 49, for "drive" read driver line 69, for "the tool to" read to the toolvto Signed and sealed this 8th day 0f January 1963o SEAL) ttest:

RNEST w. SWIDER DAVID LI LADD Lttesting` Officer Commissioner of Patents 

